Rotary electric machines including electric motors, generators, and the like have employed various cooling methods including air cooling and liquid cooling. Liquid cooling is used to help make motors smaller and to remove the heat more efficiently.
The most common liquid cooling design uses a cooling jacket wrapped around the outside of the stator assembly. This can be seen in U.S. Pat. No. 5,448,118, included herein by reference. In this design there is an aluminum extrusion that surrounds the outside of the stator and has passages for cooling fluid to pass through. This design cools the stator better than air, but is limited by i) the conductivity between the jacket and the stator, ii) the poor conductivity of the stator laminations, iii) the conductivity of the slot liners, and iv) the poor conductivity between the winding and the slot liners.
Another method that is commonly used is passing cooling through the stator laminations or into slots cut into the stator laminations. Either of these has similar disadvantages to the cooling jacket design.
Further, some techniques involve spraying fluid directly on the stator or submerging the stator. These have the disadvantage of either being complex or having the fluid cause drag between the rotor and the stator.
There are a couple of techniques to place the cooling jacket through the winding slot. One of these is forcing fluid down the center of a conductor. Typically the fluid in this case is a non-conductive oil. This has the disadvantage of requiring a special fluid and some complex manufacturing methods to provide the fluid channel. Other techniques place a pipe or vessel down through the slot with cooling fluid in it. These typically also use non-conductive oil and have non-conductive connections to a manifold at their end. An example of this can be found in U.S. Pat. No. 3,112,415, incorporated herein by reference.
Rotary electric machines including electric motors, generators, and the like have also employed various types of stator windings.
The most common stator winding type is an integer-slot winding wherein the number of slots per pole per phase is an integer. An example of this is a 4 pole 12 slot, 3 phase motor. The number of slots per pole per phase is 1 and therefore an integer. These windings typically require some relatively complex end turns to wire them properly.
Another type of winding is a fractional-slot winding. When the number of slots per pole per phase is a fraction greater than one, this is called a fractional-slot winding. This also has complicated end turns and has the disadvantage of being less efficient. It is sometimes used to smooth out torque ripple or for other specific applications.
The third type of winding is a concentrated winding when the number of slots per pole per phase is a fraction less than one. These can also be called non-overlapping concentrated windings. They have the disadvantage of decreasing the inherent efficiency of the device, but make the end turns very simple and can facilitate other advantages. An example of a concentrated winding would be an 8 pole, 9 slot, 3 phase machine. The number of slots per pole per phase is 0.375 in this case. The fundamental power from this configuration is reduced by 5.5%. Concentrated windings can be single layer or double layer designs. Single layer designs have windings that are wound only on alternating stator teeth and only apply where there is an even number of stator slots/teeth. Double layer designs have coils wound on every stator tooth. In this configuration, there is a coil that surrounds each of the teeth on the stator and there is the same number of coils as slots. In this configuration, each slot has half of one coil and half of another coil going through the slot and the end turns are very short. Ideally, the end turns can be as short as the width of the stator tooth.
Rotary electric machines including electric motors, generators, and the like have also employed various methods of constructing stator windings.
One common method is random winding. This method can use rectangular or round wire, but typically uses round wire. Here the windings are placed by the winding machine with the only requirement that they be located in the correct slot. This is the easiest method of stator winding, but results in the lowest amount of conductor in the slot and therefore the lowest efficiency.
Another common method is traditional form winding. This method typically uses rectangular wire with mica tape located between conductors to separate any conductors that are significantly different in voltage. This insures a robust winding for higher voltage machines or machines that are prone to partial discharge. This is the most labor-intensive type of winding and is typically used in machines that are less cost sensitive.
One winding type that is not typical in motors, is used in certain types of transformers, chokes, and inductors is bobbin layer winding. This type of winding places conductors in exact locations for very accurate stacking of wires. This can achieve a high amount of conductors in a small area for high efficiency. This is not typically used for stator windings because it is not typical to be able to bobbin wind a coil and then insert it into a stator assembly. In the few cases where it is used with a conventional stator, the insertion of the coil into the stator will jumble the wires to render it similar to a random wound coil.